1. Field
Embodiments discussed herein relate to an AC-DC converter having an inrush current limiting function.
2. Description of the Related Art
In general, in electric/electronic apparatuses, to supply the voltage needed, an AC-DC converter (a power converting apparatus) capable of converting commercial AC power into a predetermined DC power for an output, may be used. The charge of a smoothing capacitor connected to an output of the AC-DC converter is about “0” (zero) before the AC power is supplied, but at the moment when the AC power is supplied to the AC-DC converter, the charge of the smoothing capacitor is turned into a state similar to the state of a short circuit, and thus a large inrush current, that is as small as tens of one ampere or greater than 100 amperes depending on a line impedance thereof, is generated.
The inrush current may be defined as the large amount of the current value that is temporarily generated in a circuit when power of an electric/electronic apparatus is turned on. When the large inrush current flows through the AC-DC converter and exceeding the limited peak current, damage may occur at a semiconductor device used at the AC-DC converter. Thus, the inrush current needs to be limited (controlled).
To limit the inrush current as such, two methods may be conventionally suggested.
FIG. 1A illustrates a conventional AC-DC converter having a current limiting function.
As illustrated on FIG. 1A, an AC-DC converter 1 includes an inrush current limiting circuit 20 configured to limit an inrush current, a diode bridge rectifier 30 configured to rectify an AC current, a boost converter 40 configured to correct a power factor, and a smoothing capacitor 50 configured to smooth the voltage passed through the boost converter 40.
The diode bridge rectifier 30 may be referred to as a bridge circuit with four diodes 32, 34, 36, and 38 connected thereto, and the diode bridge rectifier 30 is configured to output a voltage having the same polarity regardless of the polarity of input voltage.
The boost converter 40 includes an inductor 42, a switch 44, and a diode 46, and may be divided into two operations, such as a motion when the switch 44 is being turned ON and an operation when the switch 44 is being turned OFF. When the switch 44 is being turned ON, a current flows at an inductor L and energy is accumulated, and the energy accumulated at the smoothing capacitor 50 is consumed at the output terminal. As the switch 44 is being turned ON, the diode 46 blocks the charge of the smoothing capacitor 50 from flowing toward the switch 44. When the switch 44 is being turned OFF, the energy accumulated at the inductor 42 is added to an input voltage, such that the voltage passing through the diode 46 is increased as much as the energy accumulated (voltage) at the inductor 42.
The inrush current limiting circuit 20 includes a resistance 22 and a switch 24 connected in parallel to the resistance 22. As illustrated in FIG. 1A, when an AC voltage is input to the AC-DC converter 1 at the time when the switch 24, inside the inrush current limiting circuit 20, and the switch 44, inside the boost converter 40, are in an OFF state, the initial inrush current flows through the resistance 22 disposed at an AC input terminal, and the smoothing capacitor 50 disposed at the output terminal of the AC-DC converter 1 is charged. That is, by having the current, which flows at an initial stage of the input of the AC voltage, flow through the resistance 22 disposed at the AC input terminal, the size of the inrush current may be limited. If the charging at the smoothing capacitor 50 is completed after a predetermined time is passed, energy may be needlessly consumed at the resistance 22. Thus, by turning ON the switch 24 connected in parallel to the resistance 22 when the size of the current introduced to the smoothing capacitor 50 is decreased upon the completion of the charging at the smoothing capacitor 50, the current flowing to the resistance 22 may be blocked, and thereby energy consumption at the resistance 22 may be reduced.
FIG. 1B is a circuit diagram of a conventional AC-DC converter including an inrush current limiting circuit.
As illustrated on FIG. 1B, a AC-DC converter 2 includes a diode bridge rectifier 30 configured to rectify an AC voltage, a boost converter 40 configured to correct a power factor, a smoothing capacitor 50 to smooth the voltage passed through the boost converter 40, and an inrush current controlling circuit 60 configured to limit an inrush current. The AC-DC converter 2, instead of the resistance 22 and the switch 24 disposed at an AC input unit of the AC-DC converter 1 illustrated on FIG. 1A, is provided with a resistance 52 and a switch 54, which are connected in parallel to each other and connected in series to the smoothing capacitor 50 of a DC terminal. The inrush current limiting circuit 60 is provided with a resistance 62 disposed thereto to detect the current flowing at a rear end of the diode bridge rectifier 30, and detects the value of the current that flows at the resistance 62 by measuring the voltage droop generated when a current flows at the resistance 62.
When the initial power is supplied, the inrush current passes through the four diodes 32, 34, 36, and 38 at the diode bridge rectifier 30, the inductor 42, the diode 46, the smoothing capacitor 50, and the inrush current limiting resistance 52. After the initial power is supplied, an inside supplementary converter (not shown) is started, and the supplementary converter (not shown) generates a bias voltage Vcc for the inrush current limiting circuit 60. A comparator 64 is configured to turn ON a switch 54 only when the current flowing at the resistance 62 is less than a predetermined value. That is, in a case when the current flowing through the resistance 62 is greater than the value that is predetermined, by turning OFF the switch 54 connected to the DC terminal, such that the initially charged current flows through the resistance 52, and when the current flowing through the resistance 62 is less than the value that is predetermined, by turning ON the switch 54 connected to the DC terminal, the current does not flow through the resistance 52, thereby limiting the size of the inrush current. The AC-DC converter 2 illustrated in FIG. 1B may be configured to detect the size of the current introduced to an inside the circuit thereof, and limit the inrush current according to the value of the current that is detected. The AC-DC converter 1 illustrated in FIG. 1A may be used in reducing the size of the current introduced to the circuit thereof by using the resistance 22.
The AC-DC converter 1 illustrated on FIG. 1A is provided with the resistance 22 and the switch 24 disposed at the input terminal thereof to limit the inrush current, but the volume that is occupied by the resistance 22 and the switch is large. As the system is includes the capacitor 50 having a large capacity thereof, the size and capacity of the switch 24 needs to be large as well. In addition, a relay, which is conventionally used as the switch 24, is provided with a mechanical contact point, where loss of energy is generated.
Since the AC-DC converter 2 illustrated on FIG. 1B includes the resistance 62 to measure, the size of the current introduced to an inside the circuit thereof, power consumption occurs at the resistance 62 and conducting loss occurs at the switch 54 of the DC terminal.
Since the control structure configured to limit the inrush current is embodied as a circuit in the AC-DC converter 2, additional circuit devices are used at the AC-DC converter 2 than with the AC-DC converter 1 illustrated on FIG. 1A. In addition, in order to control (change) the inrush current limiting unit 60 having various circuit devices or to add new functions to the inrush current limiting unit 60, an improved inrush current limiting unit 60 is needed.